Moves monitoring of the agent v2 API connection to the yamux layer.
Present behavior monitors this at the websocket layer, and closes the websocket on completion. This can cause yamux to hit unexpected errors since the connection is closed underneath it.
This might be the cause of yamux errors that some customers are seeing
In any case, it's more graceful to close yamux first and let yamux close the underlying websocket. That should limit yamux error logging to truly unexpected/error cases.
The only downside is that the yamux `Close()` doesn't accept a reason, so if the agent becomes outdated and we close the API connection, the agent just sees the connection close without a reason. I'm not sure we log this at the agent anyway, but it would be nice. I think more accurate logging on Coderd are more important.
I've also added some logging when the monitor disconnects for reasons other than the context being canceled (e.g. agent outdated, failed pings).
Refactors the code that handles monitoring an agent websocket with pings and updating the connection times in the DB.
Consolidates v1 and v2 agent APIs under the same code for this.
One substantive change (not _just_ a refactor) is that I've made it so that we actually disconnect if the agent fails to respond to our pings, rather than the old behavior where we would update the database, but not actually tear down the websocket.
Spike Curtis
Cian Johnston
Steven Masley
